1. Field of the Invention
The present invention relates to non-destructive inspection of turbine components. More specifically, the invention provides inspection heads for positioning sensing elements on the surface of turbine rotor discs on either a fully assembled rotor or on discs that have been removed from the rotor in a controlled, repeatable manner.
2. Description of the Related Art
The blades of steam turbines are attached to discs and are subjected to significant stress due to the heat, pressure, and vibrations within their operating environments. It is therefore necessary to periodically inspect these discs for surface cracking, internal cracking, and pitting at the blade attachment area and the rotor attachment area, known as the disc bore. If such inspections locate indications of defects beginning to form that are not sufficient to take the disc out of service, it is desirable to ensure that later inspections focus on locations within the discs where the indications were found in the previous inspection.
Turbine discs are presently inspected using sensing elements such as ultrasonic probes and eddy current probes, the operation of which is well known in the art. Presently used probes are hand held, thereby limiting the positional accuracy of the inspection, and the repeatability with which the probes may be positioned.
Accordingly, there is a need for a means of accurately and repeatably positioning an inspection probe in a desired location with respect to a turbine disc. There is an additional need for such probes to fit within the small space available between discs within a typical turbine rotor assembly, thereby avoiding a need to remove the discs from the turbine for inspection.